Spray type dampeners have been known and used for many years to dampen the plates of lithographic printing presses. Most of them employ revolving brushes with a coacting pan roller, deflector blades or the like to generate the required spray which is directed toward the plate cylinder and the volume of spray is regulated by varying the speed of the rotating brush and/or by adjusting the position of the deflector blades. The known devices have not been satisfactory, however, because of their inability to generate a consistently uniform spray at all press speeds. Each such device has an optimum brush speed and/or deflector blade setting at which it will generate a spray having the required particle size and density and, therefore, if the speed of the brush or the position of the deflector blade is changed to accommodate a change in press speed, the characteristics of the spray are changed, usually with adverse effects upon the quality of the printed product.
A further disadvantage of the known dampeners resides in the fact that the brush bristles not only become contaminated with ink after short periods of operation, but they are also subject to relatively rapid wear and each such condition produces a change in the characteristics of the spray. As a result, relatively frequent readjustments or replacements of the brush are required to obtain reasonably consistent results.
In some instances, manually adjustable baffles have been used, either alone or in combination with brush speed adjustments, to regulate the volume of spray. Such means also have proved to be unsatisfactory because initial adjustments and frequently, repeated readjustments of the baffles are required each time the press speed is changed and before the proper ink/water balance is achieved. In a multi-unit press such practice requires the manual adjustment of a substantial number of baffles which is not only tedious and time consuming, but also results in substantial amounts of waste before the required settings are achieved.